Microwave apparatus using multiple avalanche diodes operating in the anomalous mode

ABSTRACT

The terminals of a first avalanche diode are shunt coupled to a microwave transmission line. The terminals of opposite polarity of at least one other avalanche diode are also shunt coupled to the microwave transmission line. Complementary microwave circuitry and proper location within a suitable microwave resonant circuit enables the multiple avalanche diodes to operate in the anomalous mode in an oscillator, amplifier, or frequency multiplier when reversed biased by an appropriate signal.

United States Patent Kawamoto MICROWAVE APPARATUS USING MULTIPLEAVALANCHE DIODES OPERATING IN THE ANOMALOUS MODE Inventor: HirohisaKawamoto, Hightstown,

Assignee: RCA Corporation Filed: March 31, 1971 Appl. No.: 129,805

Related US. Application Data Continuation-in-part of Ser. No. 102,390,Dec. 29, 1970, abandoned.

u.s. c1 ..331/107 R, 321/69, 330/56,

331/96, 331/101, 333/7, 333/84 M 1m. 01. ..I-l03b 7/06 Field of Search..331/96, 101, 10?; 321/69;

[451 Aug. 8, 1972 References Cllted OTHER PUBLICATIONS ElectronicEngineer, Diode RF Sources" by Dr. A. I. Zverev, pages 45- 50, Feb.i969.

Primary Examiner-John Kominski AttorneyEdward J. Norton [57] ABSTRACTThe terminals of a first avalanche diode are shunt coupled to amicrowave transmission line. The terminals of opposite polarity of atleast one other avalanche diode are also shunt coupled to the microwavetransmission line. Complementary microwave circuitry and proper locationwithin a suitable microwave resonant circuit enables the multipleavalanche diodes to operate in the anomalous mode in an oscillator,ampli fier, or frequency multiplier when reversed biased by anappropriate signal.

7 Claims, 7 Drawing Figures PATEmEnwc 8 m2 3.683.298

lia. l.

IN VENTOR. Hirolzisa K awamoto TTORNEY PIITENTIiIIaus 8 m2 SHEET 2 IIF 3REVERSE BIAS SIGNAL MICROWAVE INPUT SIGNAL REVERSE BIAS SIGNAL TERMINA-TION GROUND -MICROWAVE INPUT SIGNAL BIN MICROWAVE UTPUT SIGNAL AOUT OGROUND TERMINATION MICROWAVE OUTPUT SIGNAL I N VENT 0R. HmoH/se k4 wmpro B Y TTORNEY MICROWAVE APPARATUS USING MULTIPLE AVALANCHE DIODESOPERATING IN THE ANOMALOUS MODE The present invention is acontinuation-in-part of application Ser. No. 102,390, filed Dec. 29,1970 and DESCRIPTION OF THE PRIOR ART The design and successfuloperation of microwave apparatus using avalanche diodes, operating inthe anomalous mode, have been published in many reports. The paper by P.A. Levine and S. G. Liu, entitled Tunable L-Band High-Power AvalancheDiode Oscillator Circuit, presented at the ISSCC Conference,Philadelphia, February 1969, describes the necessary boundary conditionswhich must be solved before an avalanche diode can be triggered intogenerating microwave oscillations in the anomalous mode. However, thedemands for increased output power from microwave sources have led tothe operation of multiple, shunt-mounted, avalanche diodes in a singlemicrowave oscillator circuit.

The use of microwave hybrids as power summers for individual sourceshave proved unsatisfactory because they increase the size and complexityof the microwave circuit. A push-pull circuit has been used foroperation of two semiconductive devices. However, such an arrangementhas the disadvantage of requiring microwave isolation betweensemiconductive devices, which is sometimes difficult to obtain.

A series coupling of avalanche. diodes for a microwave source has thelimitation of making it difficult to provide a proper heat sink, causingdiode burn out problems if the heat sink is not sufficient. A parallelarrangement of avalanche diodes is more satisfactory, but the simpleaddition of shunt-mounted avalanche diodes will not solve all thepeculiar boundary conditions required of avalanche diodes operating inthe anomalous mode.

SUMMARY OF THE INVENTION The terminals of a first avalanche diode areshunt coupled across a microwave transmission line..The terminals of atleast one other avalanche diode are also shunt coupled across themicrowave transmission line. The terminal polarity of the otheravalanche diode is opposite to the terminal polarity of the firstavalanche diode.

A reverse bias signal, exceeding a predetermined threshold level, iscoupled across the terminals of each diode for triggering them intooperating in the anomalous mode at one or more desired microwavefrequencies.

The electrical separation between the first avalanche diode terminalsand the other avalanche diode terminals is substantially M2, where )t isthe wavelength at a certain desired frequency of operation.

. A microwave resonant circuit is coupled to the microwave transmissionline containing the avalanche diodes. The resonant circuit will transmitenergy at one or more desired frequencies, which may include thefundamental and/or one or more harmonics thereof,

and reflect energy at other undesired harmonics thereof.

The microwave resonant circuit is electrically positioned so that thereflected energy will have the proper phase to aid in triggering theavalanche diodes into the anomalous mode of operation.

Further features and advantages of the invention will become morereadily apparent from the following description of specific embodiments,as shown in the accompanying drawings in which:

BRIEF DESCRIPTION OF Til-IE DRAWINGS FIG. 1 is a schematicrepresentation of a microwave avalanche diode apparatus utilizingconcepts of the disclosed invention,

FIG. 2 is a cross-sectional view of a coaxial avalanche diode oscillatorusing two avalanche diodes reversed biased to operate in the anomalousmode,

' FIG. 3 is a schematic representation of a microwave avalanche diodeamplifier utilizing concepts of the disclosed invention,

FIG. 4 is a top view of a microstrip avalanche diode amplifier using twoavalanche diodes reversed biased to operate in the anomalous mode,

FIG. 5 is a schematic representation of a microwave amplifier multiplierutilizing concepts of the disclosed invention,

FIG. 6(a) is atop view of a microstrip diplexer, 7

FIG. 6(b) is a plot of Attenuation v. Frequency Characteristics of themicrowave diplexer.

Referring to FIG. 1, there is shown a' schematic representation of amicrowave apparatus incorporating the features of the present invention.The diodes D and D are avalanche diodes shunt coupled to a microwavetransmission line 16. The terminal polarity of diode D is opposite tothe terminal polarity of diode D The avalanche diodes are separated byan electrical length which is substantially M2, where A is thewavelength at a desiredfrequency of oscillation. This is illustrated inFIG. 1, by the microwave coupling of the anode l2 and cathode ll ofdiode D to the cathode l4 and the anode 13 of diode D via the microwavetransmission line 16 and the microwave bypass capacitor 15.

The avalanche diode operating in the anomalous mode, within anappropriate microwave circuit, is a two terminal negative resistancesemiconductive device. An applied reverse bias signal, slightly greaterthan the breakdown voltage of the diode, will cause a displacementcurrent or electric field in the depletion layer of the diodessemiconductive material. The diode carriers are ionized at the point ofmaximum electric field within the depletion layer. The carrier densityis increased when the ionized carriers collide with other atoms andcreate more carriers. The displacement current can also be considered asa wavefront, moving with a specific wave velocity, provided thedisplacement current has a very fast rise time. If the wave velocity ofthe displacement current is greater than the saturation velocity of thecarriers, a high density of holes and electrons will be left in the wakeof this wavefront. As a result of the concentration of holes andelectrons, the electric field is reduced and the velocity of thecarriers is diminished, leading to the formation of a dense plasma.Microwave energy is obtained from an avalanche diode by extraction ofenergy from the trapped plasma.

The necessary fast rise time of the displacement current can be achievedby utilizing the high frequency signals created by ionization at lowcurrents. The high frequency signals trigger the avalanche diode into ahigh efficiency mode of operation, the anomalous mode. The avalanchediode then emits energy at a frequency which is related to the ratio ofthe depletion layer width to the velocity of the carriers in the plasma,and the design of the complementary microwave circuitry.

A reverse bias signal is applied to the anode 13 of diode D through abiasing circuit that would prevent the leakage of microwave energy intothe bias power supply not shown. Such a biasing circuit may be a highinductance lead 17 that will appear as an open circuit at microwavefrequencies. The microwave bypass capacitor 15 will allow the appliedreverse bias signal to reverse bias both diodes, D and D The magnitudeof the applied bias signal is sufficient to trigger each respectivediode, D and D into generating microwave energy in the anomalous mode ofoperation. Diode D generates a negative going microwave pulse, B. Partof the negative going pulse, B, is transmitted along the microwavetransmission line 16 toward diodeD and part toward the microwaveresonant circuit 19.

The terminal polarity of diodeD is arranged so that the negative goingpulse, B, aids the applied reverse bias signal in triggering diode Dinto operating in the anomalous mode. Diode D generates a positive goingmicrowave pulse X, which is transmitted along the microwave transmissionline 16 toward diode D The microwave resonant circuit 19 transmitsenergy at one or more desired frequencies and appears as a microwaveshort circuit at undesired frequencies harmonically related to thedesired frequency or frequencies. Therefore, the microwave resonantcircuit 19 reflects the undesired harmonic energy contained in thenegative going pulse B, back toward the terminals of diode D The shortcircuit effect of the microwave resonant circuit 19 inverts thereflected portion of the negative going pulse B to a positive goingpulse Y. It is necessary that the positive going pulse Y and thepositive going pulse X be in phase at the terminals of diode D,. This isaccomplished by making the electrical length between diodes D and Dequal to the electrical length between the reflection plane of themicrowave resonant circuit 19 and diode D The combination of thereflected positive going pulse, X, and the generated positive goingpulse, Y, aid in triggering the next cycle of microwave oscillation fromdiode D At a particular resonant frequency of interest of the microwaveoscillator, the frequency depends on the round trip delay time requiredfor a microwave signal generated by a first diode to aid in triggering asecond diode and return to the first diode to repeat the cycle. A way tosatisfy this condition is to make the particular resonant frequencydependent on the electrical length between avalanche diodes, D and D andthe electrical length between the reflective plane of the resonantcircuit 19 and the closest diode, D The electrical length, S, betweenavalanche diodes is where A is the wavelength in the media of microwavetransmission at this frequency of interest. The internal delay time, 1is the time required of an avalanche diode before it can be triggeredinto operation. V is the phase velocity in the media of microwavetransmission. Since the product 1,, V,, is relatively small, where )t islarge at low microwave frequencies such as 800 mhz, the spacing S issubstantially M2. The electrical length, S, between the closest diode Dand the reflective plane of the resonant circuit 19 is The product (7,,V /2) is also negligible in the same frequency range and may beneglected. I

Referring to FIG. 2, there is shown a cross section of a coaxialtransmission line circuit using the techniques of the present invention.The anode 12 of diode D and the cathode 14 of diode D are both coupledto the center conductor of the same coaxial transmission line 16. Thecathode 11 of diode D is connected directly to the outer or groundconductor 20 of the coaxial transmission line. The physical spacingbetween diodes, D and D is 12 cm which is equivalent to an electricalspacing of M2 'r V where A is the wavelength in free space at 1.0 Ghz,and 1,, 0.1 nsec. A microwave bypass capacitor 15, with a parallel platecapacitance of approximately 50 pf. at 1.0 Ghz, is formed by inserting a1 mil thick piece of mica dielectric 24 between the anode 13 of diode Dand the ground conductor 20 of the coaxial transmission line.

A variable tuning capacitor 19 suitable for operating at microwavefrequencies and having a tuning range from 0.6 to 6.0 pf. is coupled inshunt between the center conductor 16 and the ground conductor 20 of thecoaxial transmission line. The tuning capacitor 19 functions as a lowpass filter. At the desired frequency of oscillation, which in this caseis the fundamental, microwave energy is transmitted to the outputconnector 23, while at harmonics of the desired frequency ofoscillation, the capacitor 19 presents a short circuit plane ofreflection. The physical spacing between the tuning capacitor 19 and thecathode 14 of D is 13.5 cm. This is equivalent to S =A/2 (r V /2).

In order to prevent the DC bias signal from being transmitted to theoutput connector 23 and yet not impede the propagation of microwaveenergy, a blocking capacitor 18 with a magnitude of 50 pf. is coupled inseries between the center conductor 16 and output connector 23. Anegative bias signal, exceeding the breakdown voltage of the diodes, iscoupled to one end of 0.25 inch length of 10 mil diameter wire 17. Theother end of the wire 17 is coupled to the anode 13 of diode D Theinductive reactance of the wire 17 is sufficient to prevent microwaveleakage back to the bias power supply not shown.

An oscillator of the type described in connection with FIG. 2 was builtand it was found that the microwave peak output power from thisoscillator was I watts at 1.0 Ghz, and the maximum efficiency was 27percent. Each diode used in this oscillator, when operated individuallyin a conventional oscillator circuit, was found to generate a peak powerof watts. The current drawn by each diode was from 2.5 to 3.5 amp., whenreversed biased to its breakdown voltage point. Each of the avalanchediodes, used in the circuit of FIG. 2 which was built, was a punchthrough pnn+ silicon mesa structure. The diameter of each of thesediodes was approximately 0.020 inch. The junction of the respectivediodes was formed by boron diffusion into nstype silicon epitaxialwafers. The resistivity of the epitaxial layer was approximately 6ohm-cm. The breakdown voltage of the respective diodes were in rangefrom 120 to 150 volts.

Referring now to FIG. 3, there is shown a schematic diagram of amicrowave amplifier. The avalanche diodes, D and D are reverse biased bya combination of DC. and microwave signals. FIG. 3 includes all theelements of the microwave oscillator of FIG. 1, which are designated byidentical reference numerals. The electrical length, S, separating theterminals of diode D from the terminals of diode D is S M2 7,, V,,,where, in this case, A is the wavelength at the frequency of themicrowave input signal. The product 7,, V, is the same as that requiredfor the microwave oscillator of FIG. 1. The addition of the circulator22, with one port coupled to the microwave resonant circuit 28, allowsan appropriate microwave input signal, applied to a second port of thecirculator, to be transmitted to the diode terminals. A DC. signalapplied at one end of the high inductance lead 17 is sufficient, in thiscase, to reverse bias the diodes, D and D to slightly below theirbreakdown voltage levels. The microwave input signal is at a desiredfrequency of operation and the positive going portion of the microwaveinput signal, A,,,, is transmitted through the microwave resonantcircuit to the terminals of diode D The positive going signal, Aincreases the existing reverse DC. bias voltage until the breakdownvoltage of diode D is exceeded. The positive going microwave signal doesnot further reverse bias diode D since the polarity of its terminals isinverted with respect to the terminal polarity of diode D The magnitudeof the microwave voltage triggers diode D into generating a negativegoing microwave pulse B The instant the negative going pulse B isgenerated, the negative going portion of the microwave input signal,B,-,,, is being propagated through the microwave resonant circuit 28.This is accomplished by making S, the electrical length from thereflective plane of the microwave resonant circuit 19 to the terminalsof both diodes, D and D The electrical length from the junction point ofthe microwave transmission lines 16 and 20 to the diode D issubstantially equal to the electrical length between the junction point10 and the reflective plane of the microwave resonant circuit 28. Thus,the negative going portion of the microwave input signal, B and thegenerated signal B are in phase at the junction point 10 and combine asmicrowave signal B which triggers diode D into generating a positivegoing microwave signal A A portion of the microwave signal, B is nottransmitted toward diode D This portion is propagated as the amplifiedmicrowave output signal through the microwave resonant circuit 28 to thethird port of the circulator 22.

A similar analysis is used with the generated positive going pulse A toexplain the dependent coupling between diodes, D and D and theirinteraction with successive cycles of the applied microwave inputsignal. The reflected harmonic energy of the pulse B combine with thepositive going pulse A and the next positive going cycle of themicrowave input signal to trigger diode D Diode D contributes thenegative going portion of the microwave output signal, B and diode Dcontributes the positive going portion of the microwave output signal,A,,,,,.

In FIG. 4, which will now be described, there is shown the top surfaceof a microstrip amplifier using the techniques of the present invention.The microstrip transmission lines 16 and 20 are conductive strips on oneside of a dielectric substrate 23. The bottom surface of the dielectricsubstrate 23 is covered by a ground planar conductor, not shown. Themicrowave resonant circuit 24 is a microstrip low pass filter thattransmits microwave energy at the frequency of the microwave inputsignal applied to the first port of the circulator 22. The low passfilter 28 presents a reflective plane at all other higher frequenciesgenerated by the avalanche diodes, D and D The low pass filter 28 andthe tuning stubs 21 match the complex impedance of the multipleconfiguration of avalanche diodes, D and D to a load impedance, notshown, terminating the third ground of the circulator 22. The cathode 14of diode D is coupled to the microstrip transmission line 16. The anode13 of diode D is coupled to one terminal of a 50 pf. bypass capacitor15. The remaining terminal of the bypass capacitor 15 is coupled to theground planar conductor. The bypass capacitor presents a low impedanceto ground for energy at microwave frequencies. One end of a 10 mildiameter, high inductance wire 17. is coupled to the anode 13 of diode DThe other end of the high inductance wire 17 is coupled to a DC. reversebias signal source, not shown. The high inductance of the 10 mildiameter wire 17 provides effective isolation of microwave leakage tothe DC. reverse bias signal source. The cathode 11 of diode D is coupledto the ground planar conductor, and the anode 12 of diode D is coupledto the microstrip transmission line 16. A 50 pf. D.C. blocking capacitor18 is coupled between the low pass filter 24 and the second port of thecirculator 22. The DC. blocking capacitor 18 presents little attenuationto microwave signals but prevents leakage of D.C. signals to thecirculator 22.

The microstrip amplifier provided a peak microwave output power of 200watts to a load terminating the third port of the circulator 22. Theavalanche diodes used in the microstrip amplifier were similar to thoseused in the microwave oscillator of FIG. 2. The avalanche diodes werereversed biased by a combination of a peak DC. voltage of volts acrosseach diode and a microwave signal of 20 watts applied to the first portof the circulator 22.

Referring to FIG. 5, there is shown a schematic diagram of a microwaveamplifier multiplier. For certain applications it may be desirable toobtain, from a microwave amplifier, a harmonic multiple of the inputfrequency. The resulting microwave output power, at this harmonicfrequency, should also have gain. The microwave amplifier multiplierillustrated by FIG. 5, uses the same basic design of FIG. 1, but withadditional elements. The theory of harmonic generation and amplificationof microwave signals by multiple avalanche diodes, operating in theanomalous mode, is unchanged from the microwave oscillator and amplifierThe electrical separation between avalanche diodes is where A is thewavelength in the media of microwave transmission at the desiredharmonic frequency of the microwave input signal. The product 1,, V isthe delay time associated with triggering the avalanche diode and thephase velocity in the media of microwave transmission. The electricalseparation between each of the avalanche diodes, D and D and thereflective plane of the microwave resonant circuit 29 is The microwaveresonant circuit 29 is a bandpass filter that is resonant at the desiredharmonic frequency and the frequency of the microwave input signal.However, the bandpass filter 29 is designed to reflect a small amount ofmicrowave energy, at these frequencies, back toward the diode terminals.At all other harmonic frequencies, the bandpass filter presents areflective plane. Each of the open circuited microwave transmission linestubs 23 have an electrical length of substantially A/2, where A is thewavelength at the desired harmonic frequency. The electrical length ofthe stubs 23 is measured from the respective diode terminals to the opencircuited terminals. The stubs 23 are used to enhance the generation andamplification of microwave energy at the desired harmonic frequency.

The microwave diplexer 24, coupled between the bandpass filter 29 andthe circulator 18, is a component that will separate the microwave inputsignal from the desired microwave output harmonic signal.

Referring to 2 6(a), there is shown, by way of example, a combination ofa microstrip bandstop filter 11 and a microstrip bandpass filter thatcompose the microwave diplexer 24. The microstrip bandpass filterelements 1, 3 and 3 are three open circuited sections of resonantmicrostrip transmission line. The gaps separating the filter elements 1,2 and 3 capacitively couple one element to the other. The center section2 is parallel to the first and third sections and substantially A/2 inlength, where A is the wavelength at the microwave input frequency. Thefirst and third sections of the bandpass filter are capacitively coupledto the center section 2 over a parallel length of substantially A/4,where A is the wavelength at the microwave input frequency.

The complementary microstrip bandstop filter 11 is anti-resonant at themicrowave input frequency. Each of the bandstop filter sections 4, 5 and6 are lengths of microstrip transmission line short circuited to groundat one end and capacitively coupled, by a small gap 8, to the maintransmission line 7 at the other end. The electrical length of thebandstop filter sections 4, 5 and 6 measured from the short circuit 9 tothe capacitive gap 8 is substantially A/4, where A is the wavelength atthe frequency of interest. The electrical separation between filtersections 4, 5 and 6 is also AM. The impedances of all he microstripfilter elements are selected to match the source impedance of themicrowave input signal.

FIG. 6(b) illustrates the attenuation, db, of a microwave signal, versusthe frequency of the microwave signal coupled to the port 25 of amicrowave diplexer. The attenuation is measured from the port 25 to thebandpass port 26 and the bandstop port 27. The microwave diplexer is abi-directional device. Any microwave signal that is coupled to port 25will propagate to port 26 with little microwave attenuation and viceversa, provided the signal is in the frequency range between f and f Thehigh reflective properties of the bandstop filter will prevent anymicrowave signal in the same frequency range, from propagating to port27. A harmonic of this frequency band, coupled to port 25, will onlypropagate to port 27. The reflective properties of the bandpass filterwill prevent this harmonic frequency from propagating to port 26.

Referring to FIG. 5, the avalanche diodes D, and D 7 are reversed biasedby a DC. signal applied to the anode 13 of diode D through the highinductance wire 17. The magnitude of the applied DC. signal is below thebreakdown voltage level of the avalanche diodes. The magnitude of themicrowave input signal applied to the first port of the circulator 22and transmitted to the diode terminals trigger the diodes, D and D intooperating in the anomalous mode. The enhanced harmonic signal and theamplified microwave input signal are propagated through the bandpassfilter 29 toward the port 25 of the microwave diplexer 24. The desiredharmonic frequency, being in the pass band of only the bandstop filter,is propagated toward a terminating load impedance, not shown, at theharmonic output port 27. The amplified microwave input signal is withinthe pass band of only the bandpass filter and is propagated through thebandpass output port 26, toward the circulator 18. The amplifiedmicrowave input signal, will propagate toward a load, not shown,terminating the output port of the circulator 18.

A new approach to the generation and amplification of microwave signalsby the use of a multiple configuration of avalanche diodes has beendemonstrated. The technique does not limit itself to only two avalanchediodes. Any number of diodes may be used as long as the conditionsillustrated by the preceding circuits are satisfied. This includesmultiple stacks of series connected diodes shunt-mounted across amicrowave transmission line in a configuration that satisfies thepeculiar boundary conditions associated with using multiple avalanchediodes operating in the anomalous mode.

A preferred embodiment of the invention in microstrip and coaxialtransmission line has been shown and described. Various otherembodiments and modifications thereof will be apparent to those skilledin the art, and will fall within the scope of invention as defined inthe following claims.

What is claimed is:

1. Microwave apparatus operative at a desired frequency, said apparatuscomprising:

first and second avalanche diodes each having terminals,

a microwave structure,

the terminals of both said first and second avalanche diodes being shuntcoupled to said microwave structure with the terminal polarity of saidfirst avalanche diode being opposite to said second avalanche diodeterminal polarity.

means for applying a reverse bias signal, exceeding a predeterminedthreshold value, across the terminals of each of said diodes, to effectsaid avalanche diodes being triggered into their anomalous mode ofoperation,

said microwave structure and said respective diodes being arranged incooperative relationship with respect to one another to provide apredetermined delay of a microwave signal propagated through saidmicrowave structure between said respective diodes, said desiredfrequency being dependent on said predetermined delay,

means for coupling a microwave resonant circuit to said microwavestructure, said circuit being resonant at 'said desiredfrequency andproviding a path of low microwave attenuation for energy at said desiredfrequency, said circuit being anti-resonant at undesired frequenciesharrnonically related to said desired frequency to thereby reflectenergy at said undesired frequencies, said diodes being positioned withrespect to said microwave resonant circuit so that said reflected energyis of proper phase to aid in triggering said avalanche diodes into theanomalous mode of operation.

2. Microwave apparatus according to claim 1, wherein said microwavestructure comprises a microwave transmission line, and wherein saiddiode arrangement comprises spacing said first and second diodes by agiven distance of said line, wherein said given distance has anelectrical length, S, of substantially,

where A is the wavelength at said desired frequency and 1-,, is theresponse time exhibited by a triggered avalanche diode in achievingoperation, and V, is the phase velocity in the media of microwavetransmission.

4. Microwave apparatus in accordance with claim 1, wherein said reversebias signal is a DC. voltage having a magnitude which in and of itselfexceeds said predetermined threshold level, whereby said avalanchediodes oscillate at said desired frequency.

5. A microwave apparatus in accordance with claim 1, wherein saidreverse bias signal is the sum of a DC. voltage having a magnitude lessthan the predetermined threshold value and the amplitude of an appliedmicrowave bias signal at said desired frequency of operation, said sumhaving a value exceeding said predetermined threshold value, wherebysaid avalanche diodes are triggered into amplifying said appliedmicrowave bias signal.

6. A microwave apparatus in accordance with claim 3, including adirectional circulator having one port coupled to said microwaveresonant circuit, said circulator having a second port for applying saidmicrowave bias signal to said avalanche diode terminals through s irnicr ave re 0 antcircuit and a third ort for a plying said ampli ledmicrowave bias sign l to a teeminating load impedance.

7. A microwave apparatus in accordance with claim l,'wherein saidreverse bias signal is the sum of a DC. voltage having a magnitude less:than the predetermined threshold value and the amplitude of an appliedmicrowave bias signal, having a given frequency, said sum having a valueexceeding said predetermined threshold value, and said apparatus furtherincluding tuning means for enhancing a desired harmonic of said givenfrequency, said harmonic being said desired frequency of operation,whereby said avalanche diodes are triggered into generating andamplifying said desired harmonic of the given frequency of saidmicrowave bias signal.

Column 5,

Column 6,

Column 7, line 12,

Column 7, line 33,

Column 7, line 37,

Column 7, line 60,

Column 10, line 1,

(SEAL) Attest:

Attesting Officer correct correct correct correct correct Signed andsealed EDWARD M.FLETCHER,JR.

ED PATENT OFF-ICE- CERTIFICATE F a CUR Patent Nofi 3,683,298

Dated August 1972 Inventor) I Hlrohlsa Kawamoto It is certified thaterror appears in theabove-identified patent and that said Letters Patentare hereby corrected as shown below:

line 2, correct "nstype" to read ntype-.

line 23, correct "ground" to read -port-.-.

first occurrence to read ---2-- "he" to read -'the--.

"S 1/2 (T V /Z" to read this 9th day of January 1973.

ROBERT GOTTSCHALK Commissioner of Patents FORM PO-IOSO (10-69) 3530 @[12USCOMM-DC 603764 159 n u s. GDVERNMENI PRINTING orncz 1969 o-3es-3:u

1. Microwave apparatus operative at a desired frequency, said apparatuscomprising: first and second avalanche diodes each having terminals, amicrowave structure, the terminals of both said first and secondavalanche diodes being shunt coupled to said microwave structure withthe terminal polarity of said first avalanche diode being opposite tosaid second avalanche diode terminal polarity. means for applying areverse bias signal, exceeding a predetermined threshold value, acrossthe terminals of each of said diodes, to effect said avalanche diodesbeing triggered into their anomalous mode of operation, said microwavestructure and said respective diodes being arranged in cooperativerelationship with respect to one another to provide a predetermineddelay of a microwave signal propagated through said microwave structurebetween said respective diodes, said desired frequency being dependenton said predetermined delay, means for coupling a microwave resonantcircuit to said microwave structure, said circuit being resonant at saiddesired frequency and providing a path of low microwave attenuation forenergy at said desired frequency, said circuit being anti-resonant atundesired frequencies harmonically related to said desired frequency tothereby reflect energy at said undesired frequencies, said diodes beingpositioned with respect to said microwave resonant circuit so that saidreflected energy is of proper phase to aid in triggering said avalanchediodes into the anomalous mode of operation.
 2. Microwave apparatusaccording to claim 1, wherein said microwave structure comprises amicrowave transmission line, and wherein said diode arrangementcomprises spacing said first and second diodes by a given distance ofsaid line, wherein said given distance has an electrical length, S, ofsubstantially, S lambda /2 - Tau d Vp where lambda is the wavelength atsaid desired frequency, Tau d is the response time exhibited by atriggered avalanche diode in achieving operation, and Vp is the phasevelocity in the media of microwave transmission.
 3. Microwave apparatusaccording to claim 1, wherein said position of said microwave resonantcircuit with respect to the closest of said diodes is determined by aneffective electrical separation, S1, of substantially, S1 lambda /2 - (Tau d Vp/2 where lambda is the wavelength at said desired frequency andTau d is the response time exhibited by a triggered avalanche diode inachieving operation, and Vp is the phase velocity in the media ofmicrowave transmission.
 4. Microwave apparatus in accordance with claim1, wherein said reverse bias signal is a D.C. voltage having a magnitudewhich in and of itself exceeds said predetermined threshold level,whereby said avalanche diodes oscillate at said desired frequency.
 5. Amicrowave apparatus in accordance with claim 1, wherein said reversebias signal is the sum of a D.C. voltage having a magnitude less thanthe predetermined threshold value and the amplitude of an appliedmicrowave bias signal at said desired frequency of operation, said sumhaving a value exceeding said predetermined threshold value, wherebysaid avalanche diodes are triggered into amplifying said appliedmicrowave bias signal.
 6. A microwave apparatus in accordance with claim3, including a directional circulator having one port coupled to saidmicrowave resonant circuit, said circulator having a second port forapplying said microwave biaS signal to said avalanche diode terminalsthrough said microwave resonant circuit and a third port for applyingsaid amplified microwave bias signal to a terminating load impedance. 7.A microwave apparatus in accordance with claim 1, wherein said reversebias signal is the sum of a D.C. voltage having a magnitude less thanthe predetermined threshold value and the amplitude of an appliedmicrowave bias signal, having a given frequency, said sum having a valueexceeding said predetermined threshold value, and said apparatus furtherincluding tuning means for enhancing a desired harmonic of said givenfrequency, said harmonic being said desired frequency of operation,whereby said avalanche diodes are triggered into generating andamplifying said desired harmonic of the given frequency of saidmicrowave bias signal.